The present invention relates to a tele-writing terminal device by which drawing information, such as that concerning texts and/or figures, as well as information concerning voice is transferred through mutual communications via a communication network such as an Integrated Service Digital Network (ISDN hereinafter), a telephone communication network, or a private line network. The present invention in particular relates to a tele-witing terminal device, a conference system being realized by interconnecting a plurality of the tele-writing terminal devices.
An example of a conference system realized by interconnecting a plurality of a tele-writing terminal devices will now be described. A plurality of documents may be simultaneously displayed commonly on the display devices associated with respective ones of the plurality of tele-writing terminal devices. In such a case, if each conference member arbitrarily and randomly specifies adding/deleting operations so as to affect the displayed documents, the displayed documents are affected in a disorderly fashion affected, resulting in confusion in the conference.
In order to prevent such confusion, the following system may be used: A concept of control right such as addition/deletion right is used so that only a tele-writing terminal device, among those holding the conference, which currently has the control right can be allowed to perform an addition/deletion operation so as to affect the common picture comprising the displayed documents. In this specification, the term addition operation means an operation, normally performed by an operator on a relevant terminal device which operation is intended to affect a picture, representing figures and/or texts, so that a certain element, comprising a line, dot, etc. for example, is added to the existing picture. Further, the term deletion operation means an operation, performance of which operation is intended to affect a picture, representing figures and/or texts, so that a certain element, comprising a line, dot, etc. for example, is removed from the existing picture. Further, the term alteration operation means an operation, performance of which operation is intended to affect a picture, representing figures and/or texts, so that the picture is magnified in size or is reduced in size or is replaced by another one stored in a predetermined storage, for example.
Another system as follows using the above proposed system may also be used: In the other system, information concerning performance of an addition/deletion operation to affect the common picture, occurring in the tele-writing terminal device not having the control right, is effectively used. That is, the addition/deletion operation information is first sent to the tele-writing terminal device having the control right, said tele-writing terminal device then determines for the sent information as follows: Said tele-writing terminal device determines whether the sent information is valid so that the corresponding addition/deletion operation is allowed to be performed so as to affect the common picture or the sent information is invalid so as to be ignored. Such a system is disclosed in Japanese Patent Laid-Open Application No.3-150939, for example.
Certain difficulties/problems may arise in such a system as that of the former example wherein only a conference member whose terminal has the control right is allowed to perform the addition/deletion operation so as to affect the common picture. Such difficulties/problems may arise, for example, when hot debate occurs in the conference. Then, transfer of the control right to the terminal of a conference member who wishes to argue by affecting the common picture is problematic.
Anther problem may occur in a system such as that of the latter example wherein a conference member whose terminal has the control right may allow/reject an addition/deletion operation, to be performed on the common picture, requested by another member whose terminal thus does not have the control right. In that case, actually, the following system may be employed in practice: First, in the terminal not having the control right, the relevant addition/deletion operation is specified by the operator temporarily so as to affect the picture displayed on the terminal's screen. Information concerning the relevant addition/deletion operation is sent to the terminal having the control right. Then, in the terminal possessing the control right, based on the received relevant information, the same addition/deletion operation is specified by the operator so as to temporarily affect the picture displayed on the terminal's screen. Then, the conference member whose terminal has the control right determines whether the relevant addition/deletion will be allowed or rejected. In the case of rejection, the temporary effect of the relevant addition/deletion operation is canceled from the picture displayed on the screen of the terminal possessing the control right. Simultaneously, information indicating the determination result of rejection is sent to the terminal not possessing the control right. Then, at the terminal not possessing the control right, based on the result of rejection, the temporary effect of the relevant addition/deletion operation is canceled also from the picture displayed on the screen of the terminal not possessing the control right. As described above, the actual process comprises a rather complicated control process.
Further, in the above system, the following difficulties/problems may arise: It may occur that respective addition/deletion operations are simultaneously specified by the corresponding operators on a plurality of terminals, each not having the control right so that the common picture is affected accordingly. In such a case, the conference member whose terminal has the control right must decide between plurality of requests.